The overall objective of this investigation is the further elucidation of the regulatory mechanisms controlling the primary cytotoxic T-lymphocyte (CTL) response. Two subsets of suppressor T-cells have been identified which act at distinct stages in CTL development--one regulating proliferation of CTL and the other their maturation. During the past year studies centered on the mechanism of action of the anti-proliferative suppressor T-cell subset and the role of H-2 antigens in its induction, specificity, and genetic restriction. These studies will be extended to the anti-differentiative suppressor T-cell subset. Furthermore, we will attempt to clone both subsets of suppressor cells by using T-cell growth factor to facilitate their propagation following activation in vitro. Others have been unsuccessful at cloning the anti-proliferative suppressor T-cell. An alternative approach will be to make T-T cell hybridomas by fusing with a T-cell tumor line, such as BW4157. Obtaining clones or hybridomas of the suppressor cell subsets would be a significant advance toward dissecting the biological and molecular basis of their function. Another course for approaching the mechanism of suppressor cell function will be to establish whether soluble factors are secreted by suppressor cells of either subset which mediate their function. Lymphocyte preparations containing activated suppressor cells are cultured in vitro. Supernatants recovered from these cultures are titrated into a primary in vitro CTL generation system to screen for inhibitory effects. Preliminary results have identified a factor produced by the anti-differentiative suppressor cell but none has been detected yet for the anti-proliferative suppressor cell. The information to be gained from these studies will be the determination of the properties, functions, and specificity of two functionally distinct subsets of suppressor T-cells that act in the immunoregulation of the primary CTL response.